Manchester Memoirs, Vol. Ix. (191 6), No. "Z. 41 



be compared with the other drawings in that figure, it 

 will be obvious that it cannot have been derived from any 

 form after Dipterus platycephalus because of the occur- 

 rence of a median element separating two principal pairs 

 of plates, which is lost in Pentlandia macropterus and 

 subsequent stages. We therefore hold that Ctenodus is 

 not closely connected with Sagenodus but represents a 

 different line long separated from it, which has a rapid 

 and different specialisation of its teeth, and is very con- 

 servative in the top of its head. Uronemus is another 

 Dipnoan which is obviously not a member of our series, 

 if the account of its teeth given by Dr. Traquair is to be 

 relied on. The specimens in Manchester of Uronemus 

 splendens only show one row of bluntly pointed apparently 

 flattened teeth the meaning of which is somewhat ob- 

 scure ; they have been regarded by Dr. Traquair and 

 Dr. Smith Woodward as marginal teeth, but the evidence 

 so far as we know it does not completely exclude of the 

 view that they really represent the larger ends of the 

 ridges of dental plates perhaps very narrow in their palatal 

 expansion and perhaps with an exaggerated row of teeth 

 along the outer edge. 



It now remains to consider the relation of the Dipnoi 

 to the Rhipidistia. We have shown that the skull of 

 Dipterus valenciennesi is the base of our series, and it is 

 the most primitive Dipnoan skull known. In Text-fig. 9 

 we have placed it alongside a representation of Osteolepis, 

 into which we have introduced the supra-orbital plate of 

 Glyptopomus, and a division of the squamosal so that it 

 includes all bones known to occur in the skull of the 

 Rhipidistia, so that it is really a schematic representation 

 of the most primitive form of skull in that order. For 

 clearness the circumorbital and cheek plates are represented 

 somewhat broadened. Comparison of these figures will 



